Non-visible areas of materials, such as the interiors of components, welds and composite materials can be analysed using ultrasonic testing. This type of non-destructive testing (NDT) utilises the reflection of sound waves to detect faults and features which would otherwise be very difficult to detect without destroying the component in the process. Ultrasonic testing is a common technique in the aerospace sector to test the integrity of materials at manufacture and during service.
Scanners tend to be of the portable type (i.e. more suited to in-service scanning) or non-portable type (specifically for production).
A feature of ultrasonic testing is that a couplant is required to aid transmission of the ultrasonic energy to the test specimen because the acoustic impedance mismatch between air and solids (i.e. such as the test specimen) is large. This causes reflection of the sound waves and a loss in scan quality if a couplant is not used. Couplants generally take the form of water or gel or a deformable solid.
Traditionally, ultrasonic testing has been limited in terms of inspection speed as the operation had to be carried out on a point-by-point basis. Improvements have led to the development of array scanning, or “paintbrush” scanning which permits a continuous scan over a surface to produce a two dimensional image of the desired region of the test component. Such equipment however is bulky and limited to use in a production (as opposed to service) environment and is not considered portable.
Scanning of radii and tightly curved areas is a problem. Defects in e.g. laminar composites often occur parallel to the surface of the workpiece. As such the ultrasonic transducer needs to have its scanning vector oriented normal to the surface of the workpiece to scan effectively.
This causes problems in tightly curved areas, and especially at tight fillet radii found for example at the root of a stringer web. Such radii are in the order of 5 mm radius and the use of traditional bulky scanners in this area is not effective. In particular, linear scanning arrays can not project ultrasonic energy normal to the surface of a curved component.
It is desirable to scan such radii at a minimum resolution of about 1 mm.
It is an aim of the invention to provide an improved inspection device.